Metal production

ABSTRACT

METAL SUCH AS ALUMINUM IS PRODUCED ELECTROLYTICALLY FROM THE METAL CHLORIDE DISSOVED IN MOLTEN SOLVENT OF HIGHER DECOMPOSITION POTENTIAL, IN A CELL WHICH INCLUDES AN ANODE, AT LEAST ONE INTERMEDIATE BIPOLAR ELECTRODE AND A CATHODE IN SUPERIMPOSED RELATIONSHIP DEFINING INTERELECTRODE SPACES, WITH BATH FLOW THROUGH THE INTER-ELECTRODE SPACES EFFECTING REMOVAL THEREFROM OF METAL PRODUCED, AND PERMITTING ACCUMULATION OF METAL BY SETTING FROM THE OUTFLOWING BATH.

July 2, 1974 M. B. DELL ETAL 3,822,l%

METAL PRODUCTIQN Filed Sept. 8, 1971 2 Sheets-Sheet l7 FIGJ.

M. B. DELL ETAL METAL PRODUCTION July 2, 1974 2 Sheets-Sheet B 7 Filed Sept. 8, 1971 Flea.

FIG.2.

United States Patent 01 fee 3,822,195 Patented July 2, 1 974 3,822,195 v METAL PRODUCTION M. Benjamin Dell, Pittsburgh, Warren E. Haupin, Lower But-rel], and Allen S. Russell, New Kensington, Pa., assignors to Aluminum Company of America, Pittsburgh, Pa. Filed Sept. 8, 1971,7Ser. No. 178,650

Int. Cl. C22d 3/00, 3/08, 3/12 US. Cl. 204-64 16, Claims ABSTRACT OF THE DISCLOSURE Metal such as aluminum is produced electrolytically from the metal chloride dissolved in molten solvent of higher decomposition potential, in a cell which includes an anode, at least one intermediate bipolar electrode and a cathode in superimposed relationship defining interelectrode spaces, with bath flow through theinter-electrode spaces effecting removal therefrom of metal produced, and permitting accumulation of metal by settling from the outflowing bath.

BACKGROUND OF THE INVENTION This invention relates to a cell and process for producing metal such as aluminum from the metal chloride dissolved in a molten solvent, by electrolyzing the chloridesolvent bath in a cell which includes an anode, at least one intermediate bipolar electrode, and a cathode in superimposed spaced relationship defining inter-electrode spaces, with selectively directed bath flow through the interelectrode spaces. While the invention may be employed for producing other metals, such as magnesium, zinc or lead, it is particularly applicable to producing aluminum.

Commercial production of aluminum is presently effected by electrolyzing a bath of alumina dissolved in a molten halide composed essentially of sodium fluoride, aluminum fluoride and calcium fluoride. In this process, commonly known as the Hall process, carbon anodes are employed which are gradually consumed by the oxygen produced on the anode surfaces, and this represents a considerable economic loss attendant upon such operations. The bath is maintained at temperatures over 900 C. Power efliciency is limited by the practicalnecessity of maintaining an anodecathode distance of at least about 1% inches (from carbon anode tothe underlying layer of molten aluminum which is the effective cathode surface), in order to reduce intermittent shorting and loss of current efficiency caused by undulations of the aluminum layer induced by magnetic fields.

The present invention is directed particularly to the use of aluminum chloride as the source material for aluminous metal. Since electrolytic reduction. of aluminum chloride does not produce oxygen, and since it may be electrolyzed at appreciably lower temperatures than alumina, two inherent economic limitations of the conventional Hall process are avoided. Although the possibilities of achieving these and other advantages attendant the use of aluminum chloride as a source materialin the electrolytic reduction of aluminum have long been recognized and avidly sought, commercial realization thereof has been precluded by numerous other unsolved problems attendant upon the use of this source material in such as process.

Among the problems to be overcome by a commercially viable process for producing aluminum from aluminum chloride by electrolysis are the achievement of high power bipolar electrodes, it is noted that such suggestions genere ally disclosed the use of such electrodes in vertical POSir tion, or in a position inclined at a substantial angle, so that metal produced on each cathode surface settled by gravity to the bottom of, the cell through each inter-elec-v trode space, while the chlorine produced on each anode surface rose out of each inter-electrode space, i.e. moved in a direction counter to the settling aluminum.

SUMMARY OF THE INVENTION This invention may be briefly described as a process and apparatus for the electrolytic production of metal such as aluminum from the metal chloride in a cell which includes an anode, at least one intermediate'bipolar electrode, and a cathode in superimposed, spaced relationship defining inter-electrode spaces therebetween. In its broad aspects, the process comprises electrolyzing bath composed essentially of the metal chloride dissolved in molten solvent of higher decomposition potential in each inter electrode space to produce chlorine on each anode surface thereof and metal on each cathode surface thereof, and establishing and maintaining a flow of bath through each inter-electrode space to effect removal therefrom of metal produced, this flow being such that it sweeps metal therewith out of each inter-electrode space. Desirably the bath flow is selectively directed into, across and out of each inter-electrode space, by utilization of the chlorine produced as the lifting gas in a gas lift pump which lifts the lighter bath upwardly while permitting heavier molten metal swept from each inter-electrode space to settle in a efficiency, desirably through relatively high current eflicidirection counter to that of the chlorine-pumped bath. 'In the practice of such process, additional metal chloride may be incrementally or continuously fed into the bath, and the bath as so maintained may be continuously re-cycled through the inter-electrode spaces. Still other aspects of the invention include novel structure and structural interrelationships for the cell and electrode components to complement and enhance the operational efficiency of the mode of operation just described.

Among the advantages of the invention are the avoidance of metal accumulation, whether as a pool or as sub stantial droplets or the like, on the cathode surfaces, thus permitting minimal anode-cathode spacing, less than /1 inch, with consequent reduced cell resistance. This means less heat generation and improved voltage efiiciency, with attendant economic advantages, especially in large multielectrode cells. The absence of substantial accumulation of metal on the cathode surfaces also means there is, in effect, no metal layer on such surfaces to be distorted by magnetic flux and no problem of variation in effective anode-cathode distance as is the case when metal layers of variable depth may accumulate. The chlorine produced continually passes out of the inter-electrode spaces as it performs its pumping action, thus also reducing cell resistance that might otherwise be contributed by the presence of a substantial accumulation of chlorine on the anode surfaces. The opportunity herein afforded to em-.

. ploy close anode-cathode spacing surprisingly leads to an overall improvement in current efficiency as well as in voltage efficiency, despite the close proximity of chlorine and aluminum in narrow inter-electrode spaces. The chlorine appears to remove aluminum oxide formed from impurities and to promote aluminum particle coalescence without causing substantial re-chlorination of the metal. Also, it has been observed surprisingly that with the employment of close anode-cathode spacing, e.g. less than inch, the attack on carbonaceous cathode surfaces that is otherwise caused by the presence of reduced alkali metalin the bath is minimized. Still further advantages flow from the low heat generated and the reduced operating tempera tures that may be employed.

1' While achieving the various advantages referred to above ma y not alorie render the electrolytic reduction 'of' aluminum from aluminum chloride a commercially viable reality, the advances herein disclosed provide an answer to fundamental problems of long standing which have impcded progress in this field and, as such, represent marked contributions to the desired attainment of the ultimate and long standing objective of providing an economically feasible and commercially viable process for the production of aluminum from aluminum chloride.

BRIEF DESCRIPTION OF DRAWINGS FIG. 4 is a left end view of the bipolar electrode shown in FIG. 2, the orientation thereof being shown by the line IVIV in FIG. 2.

. DETAILED DESCRIPTION OF THE INVENTION Cell Structure A preferred cell structure for producing aluminum in accordance with the principles of the invention is illustrated in the drawings. Referring particularly to FIG. 1, the cell illustrated includes an outer steel shell 1, which is lined with refractory sidewall and end wall brick 3, made of thermally insulating, electrically non-conductive material which is resistant to molten aluminum chloridecontaining halide bath and the decomposition products thereof. The cell cavity accommodates a sump 4 in the lower portion for collecting the aluminum metal produced. The sump bottom 5 and walls 6 are preferably made of graphite. The cell cavity also accommodates a bath reservoir 7 in its upper zone. The cell is enclosed by a refractory roof 8, and a lid 9. A first port 10, extending through the lid 9 and roof 8, provides for insertion of a vacuum tapping tube down into sump 4, through an internal passage to be described later, for removing molten aluminum. A second port 11 provides inlet means for feeding aluminum chloride into the bath. A third port 12 provides outlet means for venting chlorine.

Within the cell cavity are a plurality of plate-like electrodes which include an upper terminal anode 14, desirably an appreciable number of bipolar electrodes 15 (four being shown), and a lower terminal cathode 16, all preferably of graphite. These electrodes are arranged in superimposed relation, with each electrode preferably being horizontally disposed within a vertical stack. The cathode 16 is supported at each end on sump walls 6. The remaining electrodes are stacked one above the other in a spaced relationship established by interposed refractory pillars 18. Such pillars 18 are sized to closely space the electrodes, as for example to space them with their opposed surfaces separated by less than inch. In the illustrated embodiment, five inter-electrode spaces 19 are formed between opposed electrodes, one between cathode 16 and the lowest of the bipolar electrodes 15, three between successive pairs of intermediate bipolar electrodes 15, and one between the highest of the bipolar electrodes 15 and anode 14. Each inter-electrode space is bounded by an upper surface of one electrode (which functions as an anode surface) opposite a lower surface of another electrode (which functions as a cathode surface), and the spacing therebetween, e.g. about /2 inch, is referred to herein as the anode-cathode distance (the electrode to electrode distance being the effective anode-cathode dis- 4 tance in the absence of a metal layer of substantial thickness). The bath level in the cell will vary in operation but normally will lie well above the anode 14, thus filling all otherwise unoccupied space therebelow within the cell.

Anode 14 has a plurality of electrode bars 24 inserted therein which serve as positive current leads, and cathode 16. has a plurality of collector bars. 26 inserted therein which serve as negative current leads, The bars 24 and 26 extend through the cell wall and are suitably insulated from the steel shell 1. I

As noted earlier, the sump 4 is adapted to contain bath and molten aluminum, and the latter may accumulate beheath the bath in the sump, during operation. Should it be desired to separately heat the bath and any metal in sump 4, an auxiliary heating circuit may be established therein.

With reference now to FIGS. 2, 3 and 4, as well as FIG. 1, the bath fiow passages will now be described. A bath supply passage, flow into which is indicated by the arrow at 30, generally extends from the upper reservoir 7 down along the right-hand side (as viewed in FIG. 1) of the superimposed electrodes, and such passage has fluid communication with each inter-electrode space 19, and desirably with the sump 4. This bath supply passage is compositely defined by a series of selectively sized and shaped openings in the sides of the electrodes. The general movement of bath will be downwardly from the right side of anode 14, as seen in FIG. 1, through a relatively wide opening in the edge of the anode 14, thus passing into the space on the right-hand side of the uppermost inter-electrode space 19. The bath flows downwardly through the bath supply passage openings on the righthand side of the next electrode to the right-hand side of the next inter-electrode space 19, and so on. A portion of such bath may flow on through the openings on the righthand side of the cathode 16 into and through the sump 4. In an exemplary construction, the bath supply passage through the marginal edges of the several electrodes may be formed by drilling round holes 31 and saw-cutting lateral slots 32. In this case, the round holes 31 are conveniently of the same diameter in all of the bipolar electrodes 15 and in the cathode 16, and such holes may conveniently accommodate insertion of a vacuum tapping tube when desired. In contradistinction therewith, the slots 32 are desirably widest in the highest bipolar electrode 15, of decreasing size in the successively lower electrodes, and narrowest in the lowest bipolar electrode 15. The slot may be omitted in the case of cathode 16, if desired. FIG. 1 schematically shows a typical size gradation of such slots, while FIGS. 2, 3 and 4 illustrate an opening 31 and slot 32 suitable for use in an intermediate bipolar electrode position. Thus, the described bath supply passage desirably has a downward size reduction suited to its function as a vertical supply header for downwardly feeding bath from reservoir 7 into each of the inter-electrode spaces 19.

In a similar manner, a bath return passage, flow from which is indicated by the arrow at 35, provides for the upward transport of the bath material to the reservoir 7 after passage thereof through the inter-electrode spaces 19, the flow being induced as described hereinafter by the gas lift pump effect of the chlorine gas internally produced, by electrolysis in the inter-electrode spaces 19. The bath return passage generally extends upwardly along the left-hand side (as viewed in FIG. 1) of each inter-electrode space 19, i.e. opposite the supply passage, and this bath return passage has fluid communication with each inter-electrode space 19 and desirably also communicates with the sump 4. Such return passage is compositely defined by selectively sized and shaped openings in the sides of the electrodes, with a relatively wide opening in the edge of anode 14. In an exemplary construction the bath return, gas lift passage through marginal edges of the several electrodes may be formed by drilling round holes 36 and saw-cutting lateral slots 37. In this case, the round holes 36 are conveniently of the same diameter in all of the bipolar electrodes 15 and such holes many "conveniently accommodate the taking of bathsamples when desired. In contradistinction therewith, the slots 37 are desirably Widest in the highest bipolar electrode 15, of decreasing size in the successively lower, electrodes, and narrowest in the lowest bipolar electrode '15. FIG.'1 schematically shows a typical size gradation of such slots, while FIGS. 2, 3 and 4 illustrate an" opening 36' and slot 37 suited for use in an intermediate bipolar electrode position. Thus the bath return, g'aslift passage desirably has anupward size increase, i.e. it is preferably larger at the uppermost bipolar electrode levels than at the lowermost bipolar electrode levels and is generally increased in size from lower to higher levels to accommodate additional chlorine and bath flowing thereintd'from successive inter-electrode spacesfl'lfhe gas lift passage openings maybe generally compositely sized to provide a passage area at each level of about 0.05 to 0.15 squafe inches per standard cubic foot per hour (s.c.f.h.) of chlorine'passing therethrough (standardized at a pressure of one atmosphere and a temperature of 70 F.). I

' The selective flow of gas and bath across each interelectrode space 19 is desirably selectively directed by the configuration of its upper or anode surface, a preferred configuration being illustrated in FIGS. 2, 3 and 4'. Each bipolar" electrode 15 has a fiat cathode surface 40, as does cathode 16, which functions as the lower bounding surface of an inter-electrode space 19; and each bipolar electrode 15 also has atransversely channelled anode surface 41, as does anode 14, which functions as the upper bounding surface of an inter-electrode space 19. The anode surface of each electrode is preferably undercut or relieved around its perimeter 42, iu the side edge portions of which bath flow passage openings 31, 32 and 36, 3 7 are provided. Such relief operates to minimize electrolysisat the perimeter of the electrodes and thereby reduces any tendency toward short circuiting at the sides and edges of the cell.

Each anode surface includes a plurality of spaced rectangular slots or channels 45 which transversely extend to the relieved side edge of each electrode at the bath return-gas lift passage side thereof. Such slots operate to conduct chlorine upwardly away from the balance ofthe lower anode surface 41 and thereby effect removal of chlorine from a location within the minimum anodecathode space to a location further from the aluminum produced on the cathode surface, with aconcomitant minimizing of re-chlo'rination of the aluminum produced. The channels 45 do not extend to the relieved edge atthe bath supply passage side but terminate in fluid communication with a common lateral connecting channel 46. The lateral channel 46 is desirably located inboard of the bath supply passage and is defined in part by a downwardly depending marginal ledge 47 serving as a gas dam to obstruct, if not effectively prevent, back flow of chlorine gas into the bath supply passage 30. Transverse and lateral channels, similar to channels 45, .46 as just described, are incorporated on the underside of each bipolar electrode 15, and are also preferably included in the lower surface of anode 14. By way of example, the anode surfaceof each .electrodedesirably has 'a total projected channel area which is substantial but constitutes less than half the total projected area of the anode surface. The slot area and depth is desirably chosen soas to readily direct the transport of chlorine away from the lowermost anode s urface 41.

v The Molten Bath I The. electrolyte employed for producing aluminum in in accordance with the subject invention normally will comprise 'a molten bath composed essentiall'yofaluminu'm chloride dissolved in one or more halides of higher decomposition potential than aluminum chloride. By electrolysis of such a bath, chlorine is produced on the anode surfaces and aluminum on the cathode surfaces of the cell electrodes. The aluminum is conveniently separated by settling from the lighter bath, and the chlorine rises to be vented from the cell. In such practice of the subject invention, the molten bath is positively circulated through the cell by the buoyant gas lift effect of the internally producedchlorine gas, and aluminum chloride is periodically-or continuously introduced into the bath to maintain the desired-aluminum chloride concentration.

--The bath composition, in addition to the dissolved aluminum chloride, will usually be made up of alkali metal chlorides, although, other alkali metal halides and alkalineearth halides, may also be employed. A presently preferred composition comprises an alkali metal chloride base composition made up of about 50-75% by weight sodium chloride and 25-50% lithium chloride. Aluminum chloride .i'sdissolved in such halide composition to provide a bath from which aluminum may be produced by electro lysis, and an aluminum chloride content of about 1% to 10% by weight of the bath will generally be desirable. As anexample, a bath analysis as follows (in percent by weight) is satisfactory: 53% NaCl, 40% LiCl, 0.5% MgCl 0.5% KCl, 1% CaCl and 5% AlCl In such bath, the chlorides other than NaCl, LiCl and AlCl may be regarded as incidental components or impurities. The bath is employed in molten condition, usually at a temperature above that of molten aluminum and in the range between 660'and 730 C., typically at about 700 C.

Process The process for producing metal from metal chloride is exemplified by the process described in the following detailed description of preferred modes of operation of the process as employed for producing aluminum in a bipolar electrode cell, it being understood that references to exemplary cell structure shown in the drawings should be taken astillustrative only. As described hereinabove, bathsuppl'ied from reservoir 7 through bath supply passage 30 is electrolyzed in each inter-electrode space 19 in a cell which includes, in superimposed, spaced relationship, an upper anode 14, at least one intermediate bipolar electrode 15 and a lower cathode 16, toproduce chlorine on each'anode surface thereof 41, and aluminum on each cathode surface thereof 40. The electrode current density mayconveniently range from about 5 to 15 amperes per square inch, the practical operating current density suited to any, particular cell structure beingreadily determined by observation of the operating conditions. The chlorine so producedis buoyant and its movement is employed to effect bath circulation, while aluminum is swept by the moving bath from the cathode surfaces and settles from the outflowing bath in a manner to be described hereinbelow. An induced flow. of molten bath into, through and out of each inter-electrode space 19 is established which sweeps aluminum produced on each cathode surface 40 through and out of each inter-electrode space 19 in a direction concurrent with the flow of the bath. This sweeping action effectively prevents aluminum from coalescing in unduly large droplets or from building up into a substantial pool or layer thickness on the cathode surfaces, and the bath flow through each inter-electrode space may maintained at a rate such that there isno substantial accumulation of aluminum therein. In any given installation',jthe practical velocity suited to. any particularcell structure and anode-eathode spacing'willbe determined byobservation of the operating conditions.

I The molten bath exiting from each inter-electrode space 19 is' effectively and positively pumped upwardly in the return passage 35, preferably by employment of the gas lift effect thereon of chlorine produced and conducted from each inter-electrode space in the same general direction'as the bath and buoyantly rising in thereturn passage 35. This, i'n turn, induces the selectively directed, concomitant flow of 'bath through the inter-electrode spaces. Preferably the bath which is upwardly moving in the return passage 35 is delivered to the reservoir 7 above 7 the anode 14, where the chlorine may be conveniently vented from the bath (at port 12) and the aluminum chloride content of the bath may be replenished (through port 11).

While the bath is being upwardly displaced in the gas lift passage 35 as described above, aluminum swept thereinto from each inter-electrode space 19 is permitted to settle in a counter current direction therein and, surprisingly, most of the aluminum may so settle without undue re-chlorination of aluminum so produced, although some aluminum may be carried upwardly with the bath to be recirculated with the bath. Conveniently, the settling aluminum accumulates in a sump 4 below the cathode 16, from which it may be tapped as desired. One practical method of removing molten aluminum is to use a vacuum tapping tube inserted into sump 4 through port and the bath supply passage 30.

As will now be apparent, the inclusion of a plurality of spaced transverse passages and associated lateral passage on the underside of anode surfaces not only accommodates the outward flow of chlorine produced without accumulation of a substantial amount of such chlorine on the lowermost anode surfaces 41, but also selectively and unidirectionally directs and channels the flow of chlorine in a substantially unobstructed manner, minimizing or preventing back flow toward the supply passage 30. The desired selectively directed chlorine flow toward the gas lift passage 35 may be established even against a flat anode surface, of course, by various means, such as temporary initial restriction of back flow in the supply passage.

The present invention as applied to aluminum, it will be observed from the foregoing description, provides both process and apparatus for producing aluminum from aluminum chloride with substantially no consumption of anode carbon by evolved oxygen, with lower heat input and lower temperatures than encountered in the Hall process, and with high power efiiciency made possible by the opportunity to employ cell design and operating conditions in which there is low cell resistance and yet minimal re-chlorination of the aluminum produced. Thus, it will now be seen that the subject invention provides a significant contribution to obtaining the long sought economic advantages in producing aluminum from aluminum chloride.

As earlier indicated, the invention may be employed for producing other metals and alloys. For example, the cell and process described in detail herein may be employed to produce magnesium. In such case the bath may be composed of magnesium chloride dissolved in molten halide of higher decomposition potential. A suitable low density composition is one made up of at least about 80% by weight, preferably about 85%, lithium chloride and at least about l /2% by weight, preferably about magnesium chloride. From such a bath, magnesium metal is produced in the manner generally described with reference to producing aluminum. If a small amount of aluminum chloride is also present, the metal produced may also contain some aluminum.

What is claimed is: 1. A process for producing metal in a cell which includes an anode, at least one intermediate bipolar electrode and a cathode in superimposed, spaced relationship defining inter-electrode spaces, which process comprises electrolyzing bath composed essentially of metal chloride dissolved in molten solvent of higher decomposition potential in each inter-electrode space, thus producing chlorine on each anode surface thereof and metal on each cathode surface thereof, and

establishing and maintaining a flow of. bath through each inter-electrode space which sweepsthe metal therewith out of each inter-electrode space without substantial accumulation of the metal on'the cathode surface thereof.

2. The process of claim 1, wherein the anode is above the cathode and the metal is heavier than the bath.

3. The process of claim 2, wherein each anode surface has channel means for receiving chlorine.

4. A process for producing aluminum in a cell which includes an anode, at least one intermediate bipolar electrode and a cathode in superimposed, spaced relationship defining inter-electrode spaces, which process comprises electrolyzing bath composed essentially of aluminum chloride dissolved in molten halide of higher decomposition potential in each inter-electrode space, thus producing chlorine on each anode surface thereof and aluminum on each cathode surface thereof, and

establishing and maintaining a fiow of bath through each inter-electrode space which sweeps the aluminum therewith out of each inter-electrode space without substantial accumulation of the aluminum on the cathode surface thereof.

5. The process of claim 4 wherein the minimum distances between opposed anode and cathode surfaces defining the inter-electrode spaces are less than inch.

6. The process of claim 4 wherein the aluminum chloride content of the bath supplied to the inter-electrode spaces is maintained between about 1 /2 and 10% by weight.

7. A process for producing aluminum in a cell which includes an anode, at least one intermediate bipolar electrode and a cathode in superimposed, spaced relationship defining inter-electrode spaces, which process comprises electrolyzing bath composed essentially of aluminum chloride dissolved in molten halide of higher decomposition potential in each inter-electrode space, thus producing chlorine on each anode surface thereof and aluminum on each cathode surface thereof, and establishing and maintaining a flow of bath through each inter-electrode space which sweeps the aluminum therewith out of each inter-electrode space without substantial accumulation of the aluminum on the cathode surface thereof, by pumping bath from each inter-electrode space upwardly by employment of the gas lift eifect thereon of the chlorine produced while permitting the aluminum swept from each inter-electrode space to settle in a direction counter to the upwardly pumped bath. 7 8. The process of claim 7 wherein aluminum settles to a sump below the cathode.

9. The process of claim 7 wherein the chlorine is conducted out of at least one inter-electrode space in the same general direction as the bath and in substantially unobstructed manner, while back flow of the chlorine is obstructed.

10. The process of claim 7 wherein the chlorine is conducted out of at least one inter-electrode space in the same general direction as the bath in a plurality of spaced passages extending above the lowermost anode surface thereof, the passages being of sufiicient size to accommodate the flow of the chlorine produced without substantial accumulation of the chlorine on the lowermost anode surface thereof.

11. A process for producing aluminum in a cell which includes an upper anode, at least one intermediate bipolar electrode and'a lower cathode in superimposed, spaced relationship defining inter-electrode spaces, which process comprises supplying molten bath composed essentially of aluminum chloride dissolved in halide of higher decomposition potential from an upper zone to each interelectrode space through a supply passage extending therebetween,

electrolyzing bath in each inter-electrode space, thus producing chlorine on each anode surface thereof and aluminum on each cathode surface thereof, establishing and maintaining a flow of bath into each inter-electrode space, through the same, and out at a location spaced from that to which bath is supplied, thus inducing concurrent flow of aluminum swept thereby out of each inter-electrode space, and lifting bath to the upper zone from each inter-electrode space through a common passage by employment of the gas lift effect thereon of the chlorine produced and conducted to such passage while permitting the aluminum produced and flowing into such passage to settle therein, in a counter current direction, to a common sump,

venting chlorine from the bath, and

replenishing the aluminum chloride content of the bath, whereby continuous circulation of bath, down from an upper zone through the supply passage, through the interelectrode spaces, and back up to the upper zone through the gas lift passage, is maintained by the flow of the chlorine produced.

12. In the production of aluminum by electrolysis of aluminum chloride in a molten bath in a cell having a plurality of substantially horizontal electrodes therein disposed in vertically spaced relationship defining interelectrode spaces, the steps of selectively directing the flow of chlorine internally produced in the inter-electrode spaces so that it flows transversely of said electrodes into a gas lift passage, and

inducing an upwardly directed flow insaid gas lift passage of bath from at least one of said inter-electrode spaces by the buoyant gas lift effect of said chlorine directed into said gas lift passage.

13. The method as set forth in claim 12 wherein the upwardly directed flow of bath induces a concomitant flow of bath into and through said inter-electrode spaces.

14. The method as set forth in claim 13 wherein the flow of bath into and through said inter-electrode spaces effects a selectively directed displacement of aluminum from the cathode surfaces of said electrodes toward said gas lift passage.

15. A process for producing magnesium in a cell which includes an anode, at least one intermediate bipolar electrode and a cathode in superimposed, spaced relationship defining inter-electrode spaces, which process comprises electrolyzing bath composed essentially of magnesium chloride dissolved in molten halide of higher decomposition potential in each inter-electrode space,

thus producing chlorine on each anode surface 10 thereof and magnesium on each cathode surface thereof, and establishing and maintaining a flow of bath through each inter-electrode space which sweeps the magnesium therewith out of each inter-electrode space without substantial accumulation of the magnesium on the cathode surface thereof. 16. A process for producing aluminum in a cell which includes an anode, at least one intermediate bipolar electrode, and a cathode in superimposed, spaced relationship defining inter-electrode spaces, which process comprises electrolyzing bath composed essentially of aluminum chloride dissolved in molten halide of higher decomposition potential in each inter-electrode space, thus producing chlorine on each anode surface thereof and aluminum on each cathode surface thereof, and

establishing and maintaining a flow of bath through each inter-electrode space for sweeping both the aluminum and the chlorine out of each inter-electrode space and into a gas lift passage without substantial accumulation of the aluminum on the cathode surface thereof, by pumping bath from each inter-electrode space upwardly in said passage by employment of the gas lift effect thereon of the chlorine produced while permitting the aluminum swept from each inter-electrode space to settle in said pasage in a direction counter to the upwardly pumped bath.

References Cited UNITED STATES PATENTS 2,468,022 4/ 1949 Blue et a1 204--244 1,545,383 7/ 1925 Ashcroft 204-244 1,545,384 7/1925 Ashcroft 204---244 3,616,441 10/1971 Priscu 204-247 FOREIGN PATENTS 687,758 2/1953 Great Britain 204-67 HOWARD S. WILLIAMS, Primary Examiner D. R. VALENTINE, Assistant Examiner US. Cl. X.R. 204-67, 70, 71

V UNITED sTA Es PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,822,195 Dated July 2, 1974 lnvent fl M. Beniamin Dell et a1 It is certif ied that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 63 Change "as" to ---a--.

C01. 1, line 70 Change "While" to --'-While--.

(SEnL) Attest:

McCOY M. GIBSON JR. Attesting Officer C. MARSHALL DANN Commissioner of Patents FOHM PC4050 I USCOMM-DC 60376-P69 9 U.S. GOVERNMENT PRINTING OFFICE: I9! 0-366-334. 

